The invention relates to a polyaspartic acid semi-interpenetrating nanometer composite hydrogel. According to a preparation method, acrylamide monomer is a nonionic monomer, is capable of improving the salt resistance of hydrogel,and increasing the mass of hydrogel; linear high molecular polyvinyl alcohol can be used for form a semi-interpenetrating polymer network, and at the same time is capableof improving the mechanical properties of composite hydrogel; the adopted mass raw material polyaspartic acid is nontoxic, harmless, and degradable, is friendly to the environment, contains a large amount of carboxyl and amide groups, and is providing molecule chains with excellent water solubility; when the content of polyaspartic acid is relatively low, the hydratability of hydrogel is improved; bentonite contains a large amount of cations, ionizationoun can be realized easily, dispersion of cations into the polymer network is capable of improving the hydrophilcity and the water absorptioncapacity of the composite material; bentonite is a salt-resistant clay, so that introduction of bentonite into the polymer network is capable of improving the salt resistance greatly.